1. Field of the Invention
The present invention relates to spinal devices and, in particular, to spinal prostheses for use with spinal fixation devices, assemblies and systems such as spinal screw and rod assemblies or systems that are attached onto a patient's spine.
2. Background Information
There are many medical situations, because of disease, injury or deformity, where it is necessary to align, hold and/or fix a desired relationship between adjacent vertebral bodies. In order to accomplish this goal, orthopedic spinal surgeons utilize spinal fixation devices, systems and/or assemblies to provide the desired relationship between adjacent vertebral bodies. Such spinal fixation devices typically include one or more spinal fixation elements, such as relatively rigid fixation rods, that are connected to adjacent vertebrae by attaching the rod to anchor devices, systems and/or assemblies affixed onto the vertebrae. The anchor devices are typically spinal bone screw assemblies that include bone screws and screw head/spinal rod connectors.
The spinal fixation rods are typically placed on opposite sides of the spinous processes of adjacent vertebrae in a substantially parallel relationship. Spinal fixation rods may have pre-determined contours according to properties of the target implantation site. Once installed, the spinal fixation rods hold the vertebrae in a desired spatial relationship. It may also be necessary in some circumstances to provide a spinal cross-connector at one or more points between the two spinal fixation rods in order to provide additional stability to the structure. Particularly, adjacent spinal fixation rod assemblies can be made more robust by using a cross-connector to bridge the pair of spinal rods. Current cross-connectors are generally rods themselves that are adapted for connection at ends thereof to the spinal rods.
There are various medical spinal procedures where cross-connectors or current spinal prostheses of any kind do not address all of the issues created by the various medical spinal procedures. One such medical spinal procedure is a spinal decompression procedure. Spinal decompression is achieved in the patient by the removal of several adjacent spinous processes and the elongation and/or stabilization of the adjacent vertebrae through the use of the spinal fixation assemblies such as indicated above (i.e. spinal rods and spinal bone screw/rod holder assemblies). This procedure, however, can contribute to overexposure of the vulnerable spinal cord as well as create the potential for post operative soft tissue cavitation. While current cross-connectors may be used for stabilization of the spinal fixation assemblies (and thus the affected vertebrae), they are not adequate to address overexposure of the vulnerable spinal cord or the potential for post operative soft tissue cavitation as a result of a spinal decompression procedure. Other known spinal devices also do not address these problems. Moreover, other medical spinal procedures may overexpose portions of the spinal cord or spinal cord area as well as create the potential for post operative soft tissue cavitation of which the known spinal devices do not address.
Accordingly, there presently exists a need for a spinal prosthesis that addresses the inadequacies of the prior art.